The Japanese Nuclear Regulation Authority (NRA) has raised the severity level of the radioactive water leak from the crippled Fukushima No. 1 power plant to 'serious' on the international scale.
The NRA has rated the severity level at three on the International Nuclear Event Scale (INES), after Tokyo Electric Power Co. (Tepco) revealed an estimated 300 tons highly radioactive water had escaped from Fukushima's steel tank, the Japan Times reports.
The announcement has made it the worst leak from containers since the incident, the report added.
The overall Fukushima nuclear crisis has been rated at the maximum level of seven, which is at par with the 1986 Chernobyl disaster in Ukraine.
NRA regulators said that the amount of the leaked radioactive substances has totaled to several thousand terabecquerels, when converted into radioactive molybdenum 99.
Meanwhile, the International Atomic Energy Agency (IAEA) has urged Japan to explain the situation more clearly and avoid sending 'confusing messages' about the disaster.
This is the first time that Japanese authorities have decided to rate the leak the INES.